The present disclosure relates to a hydraulic control device for an automatic transmission mounted on an automobile, and specifically relates to a control device for line pressure that is hydraulic pressure for operating the respective friction engagement elements of an automatic transmission.
In the related art, a primary regulator valve regulates pump pressure from an oil pump to generate line pressure. In the primary regulator valve, basically, biasing force of a spring and throttle pressure from a throttle valve act against feedback pressure of the line pressure acting on a spool, whereby the line pressure is set based on a linear function defined by the minimum proof pressure and the maximum proof pressure (see Japanese Patent Application Publication No. 1-238750 and Japanese Patent Application Publication No. 2009-97696).
In general, the minimum pressure of the line pressure is set to be equal to or higher than a hydraulic pressure for obtaining a drive force (evacuation drive force) to ensure that the vehicle can at least travel minimally in case of a failure. Japanese Patent Application Publication No. 2009-97696 discloses a linear solenoid valve of a normally open type.